Filter media suitable for hydraulic applications

ABSTRACT

Filter media, including those suitable for hydraulic applications, and related components, systems, and methods associated therewith are provided. The filter media described herein may include two or more layers, at least one of the layers having a relatively high percentage of microglass fibers. Additionally, the filter media may be designed such that the ratio of average fiber diameters between two layers is relatively small, which can lead to a relatively low resistance ratio between the layers. The filter media has desirable properties including high dirt holding capacity with low basis weight and a low resistance to fluid flow. The media may be incorporated into a variety of filter element products including hydraulic filters.

FIELD OF INVENTION

The present invention relates generally to filter media which may beused in hydraulic applications and, more particularly, to multilayeredfilter media which have desirable performance characteristics.

BACKGROUND

Filter media can be used to remove contamination in a variety ofapplications. Depending on the application, the filter media may bedesigned to have different performance characteristics. For example,filter media may be designed to have performance characteristicssuitable for hydraulic applications which involve filteringcontamination in pressurized fluids.

In general, filter media can be formed of a web of fibers. For example,the web may include microglass fibers amongst other components. Thefiber web provides a porous structure that permits fluid (e.g.,hydraulic fluid) to flow through the filter media. Contaminant particlescontained within the fluid may be trapped on the fibrous web. Filtermedia characteristics, such as fiber diameter and basis weight, affectfilter performance including filter efficiency, dirt holding capacityand resistance to fluid flow through the filter.

There is a need for filter media that can be used in hydraulicapplications which has a desirable balance of properties including ahigh dirt holding capacity and a low resistance to fluid flow across thefilter media.

SUMMARY OF THE INVENTION

Filter media, including those suitable for hydraulic applications, andrelated components, systems, and methods associated therewith areprovided.

In one set of embodiments, a series of filter media are provided. In oneembodiment, a filter media includes at least two layers. A first layerof the filter media comprises at least 80 wt % glass fibers, wherein thefibers in the first layer have a first average diameter. The filtermedia also includes a second layer directly adjacent the first layer,the second layer comprising glass fibers, wherein the fibers in thesecond layer have a second average diameter. The second average diameteris smaller than the first average diameter. A normalized resistanceratio of the second layer to the first layer is between 1:1 and 5:1.

In another embodiment, a filter media includes at least three layers. Afirst layer of the filter media comprises glass fibers, the fibers inthe first layer having a first average diameter. A second layer of thefilter media comprises glass fibers, the fibers in the second layerhaving a second average diameter, wherein the second average diameter issmaller than the first average diameter. A third layer of the filtermedia comprises glass fibers, the fibers in the third layer having athird average diameter, wherein the third average diameter is smallerthan the second average diameter. The second layer may be directlyadjacent the first and third filter layers. A normalized resistanceratio of the second layer to the first layer is between 1:1 and 15:1.

In another embodiment, a filter media includes at least three layers. Afirst layer of the filter media comprises glass fibers, the fibers inthe first layer having a first average diameter. A second layer of thefilter media is adjacent the first layer and comprises glass fibers, thefibers in the second layer having a second average diameter. A thirdlayer of the filter media is adjacent the second layer and comprisesglass fibers, the fibers in the third layer having a third averagediameter. The filter media has an absolute specific capacity at 10microns of greater than about 2.65.

In another embodiment, a filter media includes at least three layers. Afirst layer of the filter media comprises glass fibers, the fibers inthe first layer having a first average diameter. A second layer of themedia is adjacent the first layer comprising glass fibers, the fibers inthe second layer having a second average diameter. The first and secondlayers have a combined basis weight of less than 75 g/m² and an absolutespecific capacity at 10 microns of greater than about 3.4.

In another embodiment, a filter media includes at least three layers. Afirst layer of the filter media comprises at least 90 wt % glass fibers,the first layer having a basis weight of greater than about 40 g/m². Asecond layer of the filter media is adjacent the first layer andcomprises at least 90 wt % glass fibers, the second layer having a basisweight of less than about 40 g/m². A third layer of the filter media isadjacent the second layer and comprises at least 90 wt % glass fibers.

In one set of embodiments, methods are provided. A method of filtering aliquid comprising passing a liquid including particulates through afilter media. The filter media can include one of the filter mediadescribed above and/or herein. For instance, the filter media mayinclude at least three layers. In one embodiment, a first layer of thefilter media comprises glass fibers, the fibers. in the first layerhaving a first average diameter. A second layer of the filter mediacomprises glass fibers, the fibers in the second layer having a secondaverage diameter, wherein the second average diameter is smaller thanthe first average diameter. A third layer of the filter media comprisesglass fibers, the fibers in the third layer having a third averagediameter, wherein the third average diameter is smaller than the secondaverage diameter. The second layer may be directly adjacent the firstand third filter layers. A normalized resistance ratio of the secondlayer to the first layer is between 1:1 and 15:1.

Other aspects, embodiments, advantages and features of the inventionwill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 shows an example of a filter media having multiple layersaccording to one set of embodiments; and

FIG. 2 shows a plot of absolute specific capacity at 10 microns versusbasis weight of the filter media for various samples, according to oneset of embodiments.

DETAILED DESCRIPTION

Filter media, including those suitable for hydraulic applications, andrelated components, systems, and methods associated therewith areprovided. The filter media described herein may include two or morelayers, at least one of the layers having a relatively high percentageof microglass fibers. Additionally, the filter media may be designedsuch that the ratio of average fiber diameters between two layers isrelatively small, which can lead to a relatively low resistance ratiobetween the layers. As described further below, the filter media hasdesirable properties including high dirt holding capacity with low basisweight and a low resistance to fluid flow. The media may be incorporatedinto a variety of filter element products including hydraulic filters.

As shown in the embodiment illustrated in FIG. 1, a filter media 10includes a first layer 20 adjacent a second layer 30. Optionally, filtermedia 10 can include a third layer 40 adjacent the second layer.Additional layers, e.g., fourth, fifth, or sixth layers, may also beincluded in some cases. The orientation of filter media 10 relative tofluid flow through the media can generally be selected as desired. Asillustrated in FIG. 1, first layer 20 is upstream of second layer 30 inthe direction of fluid flow indicated by arrow 50. In other embodiments,however, first layer 20 is downstream of the second layer in thedirection of fluid flow through the filter media.

As used herein, when a layer is referred to as being “adjacent” anotherlayer, it can be directly adjacent the layer, or an intervening layeralso may be present. A layer that is “directly adjacent” or “in contactwith” another layer means that no intervening layer is present.

In some cases, each of the layers of the filter media has differentcharacteristics and filtration properties that, when combined, result indesirable overall filtration performance, for example, as compared to afilter media having a single-layered structure. For example, in one setof embodiments, first layer 20 is a pre-filter layer (also known as an“loading layer”) and second layer 30 is a main filter layer (also knownas an “efficiency layer”). Generally, a pre-filter layer is formed usingcoarser fibers, and therefore has a lower resistance to fluid flow, thanthat of a main filter layer. The one or more main filter layers mayinclude finer fibers and have a higher resistance to fluid flow thanthat of a pre-filter layer. As such, a main filter layer can generallytrap particles of smaller size compared to the pre-filter layer. Wherethird layer 40 is present, the third layer may be an additional mainfilter layer that has the same or different properties as second layer30. For example, the third layer may have even finer fibers and a higherresistance to fluid flow than that of second layer 30.

The filter media can also have other configurations of first, second,and optionally third or more layers. For instance, in some cases filtermedia 10 does not include a pre-filter layer. In some such embodiments,first layer 20 is an upstream main filter layer and second layer 30 is amain filter layer downstream of the first layer. Optionally, the filtermedia can include third layer 40 (e.g., another main filter layer)positioned downstream of the second layer. An upstream layer may havecoarser fibers, and therefore a lower resistance to fluid flow, thanthat of a layer downstream of that layer. In some cases, the resistanceof each layer increases successively from the furthest upstream layer tothe furthest downstream layer.

In some embodiments, a layer having relatively coarse fibers may bepositioned between two layers having relatively finer fibers. Otherconfigurations are also possible. Additionally, a filter media mayinclude any suitable number of layers, e.g., at least 2, 3, 4, 5, 6, 7,8, or 9 layers, depending on the particular application and performancecharacteristics desired.

As noted above, each of the layers of the filter media can havedifferent properties. For instance, the first and second layers caninclude fibers having different characteristics (e.g., fiber diameters,fiber compositions, and fiber lengths). Fibers with differentcharacteristics can be made from one material (e.g., by using differentprocess conditions) or different materials (e.g., glass fibers,synthetic fibers, and combinations thereof). Without wishing to be boundby theory, it is believed that a filter media having a multilayeredstructure with layers including different characteristics exhibitssignificantly improved performance properties such as dirt holdingcapacity and/or efficiency compared to a filter media having asingle-layered structure.

In certain embodiments, one or more layers of filter media 10 includesmicroglass fibers, chopped strand glass fibers, or a combinationthereof. Microglass fibers and chopped strand glass fibers are known tothose skilled in the art. One skilled in the art is able to determinewhether a glass fiber is microglass or chopped strand by observation(e.g., optical microscopy, electron microscopy). Microglass fibers mayalso have chemical differences from chopped strand glass fibers. In somecases, though not required, chopped strand glass fibers may contain agreater content of calcium or sodium than microglass fibers. Forexample, chopped strand glass fibers may be close to alkali free withhigh calcium oxide and alumina content. Microglass fibers may contain10-15% alkali (e.g., sodium, magnesium oxides) and have relatively lowermelting and processing temperatures. The terms refer to the technique(s)used to manufacture the glass fibers. Such techniques impart the glassfibers with certain characteristics. In general, chopped strand glassfibers are drawn from bushing tips and cut into fibers in a processsimilar to textile production. Chopped strand glass fibers are producedin a more controlled manner than microglass fibers, and as a result,chopped strand glass fibers will generally have less variation in fiberdiameter and length than microglass fibers. Microglass fibers are drawnfrom bushing tips and further subjected to flame blowing or rotaryspinning processes. In some cases, fine microglass fibers may be madeusing a remelting process. In this respect, microglass fibers may befine or coarse. As used herein, fine microglass fibers are less than 1micron in diameter and coarse microglass fibers are greater than orequal to 1 micron in diameter.

The microglass fibers of one or more layers can have small diameterssuch as less than 10.0 microns. For example, the average diameter of themicroglass fibers in a layer may be between 0.1 microns to about 9.0microns; and, in some embodiments, between about 0.3 microns and about6.5 microns, or between about 1.0 microns and 5.0 microns. In certainembodiments, the microglass fibers may have an average fiber diameter ofless than about 7.0 microns, less than about 5.0 microns, less thanabout 3.0 microns, or less than about 1.0 microns. Average diameterdistributions for microglass fibers are generally log-normal. However,it can be appreciated that microglass fibers may be provided in anyother appropriate average diameter distribution (e.g., Gaussiandistribution).

The microglass fibers may vary significantly in length as a result ofprocess variations. The aspect ratios (length to diameter ratio) of themicroglass fibers in a layer may be generally in the range of about 100to 10,000. In some embodiments, the aspect ratio of the microglassfibers in a layer are in the range of about 200 to 2500; or, in therange of about 300 to 600. In some embodiments, the average aspect ratioof the microglass fibers in a layer may be about 1,000; or about 300. Itshould be appreciated that the above-noted dimensions are not limitingand that the microglass fibers may also have other dimensions.

Coarse microglass fibers, fine microglass fibers, or a combination ofmicroglass fibers thereof may be included within a layer. In someembodiments, coarse microglass fibers make up between about 20% byweight and about 90% by weight of the glass fibers. In some cases, forexample, coarse microglass fibers make up between about 30% by weightand about 60% by weight of the glass fibers, or between about 40% byweight and about 60% by weight of the glass fibers. For certainembodiments that include fine microglass fibers, the fine microglassfibers make up between about 0% and about 70% by weight of the glassfibers. In some cases, for example, fine microglass fibers make upbetween about 5% by weight and about 60% by weight of the glass fibers,or between about 30% by weight and about 50% by weight of the glassfibers.

The chopped strand glass fibers may have an average fiber diameter thatis greater than the diameter of the microglass fibers. In someembodiments, the chopped strand glass fiber has a diameter of greaterthan about 5 microns. For example, the diameter range may be up to about30 microns. In some embodiments, the chopped strand glass fibers mayhave a fiber diameter between about 5 microns and about 12 microns. Incertain embodiments, the chopped strand fibers may have an average fiberdiameter of less than about 10.0 microns, less than about 8.0 microns,less than about 6.0 microns. Average diameter distributions for choppedstrand glass fibers are generally log-normal. Chopped strand diameterstend to follow a normal distribution. Though, it can be appreciated thatchopped strand glass fibers may be provided in any appropriate averagediameter distribution (e.g., Gaussian distribution). In someembodiments, chopped strand glass fibers may have a length in the rangeof between about 0.125 inches and about 1 inch (e.g., about 0.25 inches,or about 0.5 inches).

It should be appreciated that the above-noted dimensions are notlimiting and that the microglass and/or chopped strand fibers may alsohave other dimensions.

In certain embodiments, the ratio between the weight percentage ofmicroglass fibers and chopped strand glass fibers provides for differentcharacteristics in the filter media. Accordingly, in some embodiments,one or more layers of filter media 10 (e.g., an upstream layer, adownstream layer, a first layer, a second layer, a third layer, etc.)includes a relatively large percentage of microglass fibers compared tochopped strand glass fibers. For example, at least 70 wt %, or at least80 wt %, at least 90 wt %, at least 93 wt %, at least 95 wt %, at least97 wt %, or at least 99 wt % of the fibers of a layer may be microglassfibers. In certain embodiments, all of the fibers of a layer aremicroglass fibers. In other embodiments, however, one or more layers offilter media 10 (e.g., an upstream layer, a downstream layer, a firstlayer, a second layer, a third layer, etc.) includes a relatively highpercentage of chopped strand fibers compared to microglass fibers. Forexample, at least 50 wt %, at least 60 wt %, at least 70 wt %, or atleast 80 wt %, at least 90 wt %, at least 93 wt %, at least 95 wt %, atleast 97 wt %, or at least 99 wt % of the fibers of a layer may bechopped strand fibers. Such percentages of chopped strand fibers may beparticularly useful in certain embodiments for micron ratings greaterthan 15 microns for Beta_((x))=200. In certain embodiments, all of thefibers of a layer are chopped strand fibers.

In some embodiments, one or more layers of filter media 10 (e.g., anupstream layer, a downstream layer, a first layer, a second layer, athird layer, etc.) includes a relatively large percentage of microglassfiber with respect to all of the components used to form the layer. Forexample, one or more layers may include at least 70 wt %, or at least 80wt %, at least 90 wt %, at least 93 wt %, at least 95 wt %, at least 97wt %, or at least 99 wt % of microglass fiber. In one particularembodiment, one or more layers includes between 90 wt % and 99 wt %,e.g., between 90 wt % and 95 wt % microglass fibers. It should beunderstood that, in certain embodiments, one or more layers of thefilter media do not include microglass fiber within the above-notedranges or at all.

Any suitable amount of chopped strand fibers can be used in one or morelayers of a filter media. In some cases, one or more layers includes arelatively low percentage of chopped strand fibers. For example, one ormore layers may include less than 30 wt %, or less than 20 wt %, or lessthan 10 wt %, or less than 5 wt %, or less than 2 wt %, or less than 1wt % of chopped strand fiber. In some cases, one or more layers of afilter media does not include any chopped strand fibers. It should beunderstood that, in certain embodiments, one or more layers of thefilter media do not include chopped strand fibers within the above-notedranges.

One or more layers of filter media 10 may also include microglass fibershaving an average fiber diameter within a certain range and making up acertain range of weight percentage of the layer. For instance, one ormore layers of a filter media may include microglass fibers having anaverage fiber diameter of less than 5 microns making up less than 50%,less than 40%, less than 30%, less than 20%, less than 10%, or less than5% of the microglass fibers of the layer. In some cases, a layerincludes 0% of microglass fibers having an average diameter of less than5 microns. Additionally or alternatively, the one or more layers of thefilter media may include microglass fibers having an average fiberdiameter of greater than or equal to 5 microns making up greater than50%, greater than 60%, greater than 70%, greater than 80%, greater than90%, greater than 93%, or greater than 97% of the microglass fibers ofthe layer. In some cases, more than one layer of a filter media includessuch properties. It should be understood that, in certain instances, oneor more layers of the filter media include microglass fibers withinranges different than those described above.

In other embodiments, one or more layers of a filter media includesrelatively fine fibers. For instance, one or more layers of the filtermedia may include microglass fibers having an average fiber diameter ofless than 5 microns making up greater than 50%, greater than 60%,greater than 70%, greater than 80%, greater than 90%, greater than 93%,or greater than 97% of the microglass fibers of the layer. Additionallyor alternatively, the one or more layers of the filter media may includemicroglass fibers having an average fiber diameter of greater than orequal to 5 microns making up less than 50%, less than 40%, less than30%, less than 20%, less than 10%, or less than 5% of the microglassfibers of the layer. In some cases, a layer includes 0% of microglassfibers having an average diameter of greater than or equal to 5 microns.In some cases, more than one layer of a filter media includes suchproperties. It should be understood that, in certain instances, one ormore layers of the filter media include microglass fibers within rangesdifferent than those described above.

In certain embodiments, regardless of whether the glass fibers in alayer are microglass or chopped fibers, one or more layers of filtermedia 10 includes a large percentage of glass fiber (e.g., microglassfibers and/or chopped strand glass fibers). For example, one or morelayers may comprise at least 70 wt %, or at least 80 wt %, at least 90wt %, or at least 95 wt % of glass fiber. In some cases, all of thefibers of a layer are formed of glass. It should be understood that, incertain embodiments, one or more layers of the filter media do notinclude glass fiber within the above-noted ranges or at all.

In some embodiments, regardless of whether the fibers in a layer areglass fibers (e.g., microglass or chopped fibers) and/or syntheticfibers, fibers having a fiber diameter less than or equal to 7 micronsmake up greater than about 60% by weight of the fibers, greater thanabout 70% by weight of the fibers, or greater than about 80% by weightof the fibers of a layer. In some cases, fibers having a fiber diameterless than or equal to 5 microns make up greater than about 60% by weightof the fibers, greater than about 70% by weight of the fibers, orgreater than about 80% by weight of the fibers of a layer. In somecases, fibers having a fiber diameter less than or equal to 3 micronsmake up greater than about 50% by weight of the fibers, greater thanabout 60% by weight of the fibers, or greater than about 70% by weightof the fibers of a layer.

In one particular set of embodiments, regardless of whether the fibersin a layer are glass fibers (e.g., microglass or chopped fibers) and/orsynthetic fibers, a filter media includes a first layer (e.g., apre-filter layer) having an average fiber diameter of between 1.0microns and 10.0 microns, e.g., between 1.0 micron and 8.0 microns. Asecond layer of the filter media (e.g., a main filter layer) may have anaverage fiber diameter of between about 1.0 micron and 9.0 microns,e.g., between 0.5 micron and 5.5 microns. If the filter media includes athird layer (e.g., downstream of the second layer), the third layer mayhave an average fiber diameter of between about 0.8 micron and 5.0microns, e.g., between 0.5 micron and 2.5 microns. Additional layers arealso possible.

In some embodiments, filter media 10 is designed such that the averagefiber diameters of each layer are different. For example, the ratio ofaverage fiber diameters between two layers (e.g., between a first layerand a second layer, between a second layer and a third layer, between afirst layer and a third layer, or between an upstream layer and adownstream layer, etc.) may be less than 10:1, less than 7:1, less than5:1, less than 4:1, less than 3:1, less than 2:1, or less than 1:1.Small differences in average fiber diameters between two layers may, insome instances, lead to relatively low resistance ratios between thelayers. In turn, relatively low resistance ratios between the layers canresult in the filter media having favorable properties such as high dirtholding capacity at relatively low basis weights, as described in moredetail below.

Alternatively, two layers may have larger differences in average fiberdiameters. For example, the ratio of average fiber diameters between twolayers (e.g., between a first layer and a second layer, between a secondlayer and a third layer, or between a first layer and a third layer,etc.) may be greater than 1:1, greater than 2:1, greater than 3:1,greater than 4:1, greater than 5:1, greater than 7:1, or greater than10:1.

In addition to or in place of glass fibers, one or more layers of thefilter media may include components such as synthetic fibers. Forinstance, one or more layers of filter media 10 may include a relativelyhigh percentage of synthetic fibers, e.g., at least 50 wt %, at least 60wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, or at least95 wt % synthetic fibers. In some cases, at least two layers of thefilter media, or the entire filter media, includes such percentages ofsynthetic fibers. Advantageously, synthetic fibers may be beneficial forresistance to moisture, heat, long-term aging, and microbiologicaldegradation. In other embodiments, synthetic fibers comprise a smallweight percentage of the filter media. For example, one or more layersof the filter media may include less than or equal to about 25 wt %,less than or equal to about 15 wt %, less than or equal to about 5 wt %,or less than or equal to about 2 wt % of synthetic fibers. In somecases, one or more layers of a filter media do not include any syntheticfiber. It should be understood that it may also be possible forsynthetic fibers to be incorporated within the filter media outside ofthe ranges disclosed. The synthetic fibers may enhance adhesion of theglass fibers within the web during processing. Synthetic fibers may be,for example, binder fibers, bicomponent fibers (e.g., bicomponent binderfibers) and/or staple fibers.

In general, the synthetic fibers may have any suitable composition. Insome cases, the synthetic fibers comprise a thermoplastic. Non-limitingexamples of the synthetic fibers include PVA (polyvinyl alcohol),polyester, polyethylene, polypropylene, and acrylic, polyolefin, nylon,rayon, and combinations thereof. It should be appreciated that otherappropriate synthetic fibers may also be used.

In one set of embodiments, the synthetic fibers are bicomponent fibers.Each component of the bicomponent fiber can have a different meltingtemperature. For example, the fibers can include a core and a sheathwhere the activation temperature of the sheath is lower than the meltingtemperature of the core. This allows the sheath to melt prior to thecore, such that the sheath binds to other fibers in the layer, while thecore maintains its structural integrity. This is particularlyadvantageous in that it creates a more cohesive layer for trappingfiltrate. The core/sheath binder fibers can be concentric ornon-concentric, and exemplary core/sheath binder fibers can include thefollowing: a polyester core/copolyester sheath, a polyestercore/polyethylene sheath, a polyester core/polypropylene sheath, apolypropylene core/polyethylene sheath, and combinations thereof. Otherexemplary bicomponent fibers can include split fiber fibers,side-by-side fibers, and/or “island in the sea” fibers.

Alternatively, one or more layers of the filter media can include otherfiber types such as cellulose pulp fibers (e.g., wood pulp fibers).

The filter media may also include a binder. The binder typicallycomprises a small weight percentage of the filter media. For example,the binder may comprise less than about 10 wt %, or less than about 5 wt% (e.g., between 2% and 5%) of the filter media. In some embodiments,the binder may be about 4 wt % of the filter media. As described furtherbelow, the binder may be added to the fibers in the wet fiber web state.In some embodiments, the binder coats the fibers and is used to adherefibers to each other to facilitate adhesion between the fibers.

In general, the binder may have any suitable composition. In someembodiments, the binder is resin-based. The binder may be in the form ofone or more components, for example, the binder may be in the form ofbicomponent fibers such as the ones described above. Though, it shouldbe understood that not all embodiments include all of these componentsand that other appropriate additives may be incorporated.

In addition to the binder, glass components, and synthetic componentsdescribed above, the filter media may include a variety of othersuitable additives (typically, in small weight percentages) such as,surfactants, coupling agents, crosslinking agents, amongst others.

The fiber media may have a variety of desirable properties andcharacteristics which make it particularly well-suited for hydraulicapplications. However, it should be understood that the filter mediadescribed herein are not limited to hydraulic applications, and that themedia can be used in other applications such as for air filtration orfiltration of other liquids and gases.

Filter media 10, including one or more layers of the filter media, canalso have varying basis weights, pore sizes, thicknesses,permeabilities, dirt holding capacities, efficiencies, and pressuredrop, depending upon the requirements of a desired application.

The overall basis weight of a filter media can vary depending on factorssuch as the strength requirements of a given filtering application, thenumber of layers in the filter media, the position of the layer (e.g.,upstream, downstream, middle), and the materials used to form the layer,as well as the desired level of filter efficiency and permissible levelsof resistance or pressure drop. In certain embodiments described herein,increased performance (e.g., lower resistance or pressure drop) isobserved when the filter media includes multiple layers having differentproperties, where each layer has a relatively low basis weight, comparedto certain single- or multi-layered media. As a result, some such filtermedia may also have a lower overall basis weight while achieving highperformance characteristics. For example, the overall basis weight of afilter media (or of two or more layers of the filter media) may rangefrom between about 20 and 200 g/m², or between about 90 g/m² and 150g/m². In some embodiments, the overall basis weight is less than about200 g/m², less than about 170 g/m², less than about 150 g/m², less thanabout 130 g/m², less than about 120 g/m², less than about 110 g/m², lessthan about 100 g/m², less than about 90 g/m², less than about 80 g/m²,less than about 70 g/m², less than about 70 g/m², or less than about 60g/m². As determined herein, the basis weight of the filter media ismeasured according to the Technical Association of the Pulp and PaperIndustry (TAPPI) Standard T410. The values are expressed in grams persquare meter or pounds per 3,000 square feet. Basis weight can generallybe measured on a laboratory balance that is accurate to 0.1 grams.

In certain embodiments, one or more of an upstream layer, a downstreamlayer, a pre-filter layer, a main filter layer, a first layer, a secondlayer, or a third layer of filter media 10 may have a relatively lowbasis weight. Decreasing the basis weight of one or more layers can, insome embodiments, allow the filter media to have additional layers(e.g., at least three layers), while keeping the overall basis weightrelatively low or within a certain range. For example, the basis weightof one or more such layers (or the combination of two or more layers)may range from between about 10 and 100 g/m², between about 20 g/m² and70 g/m², or between about 20 g/m² and 50 g/m². In some embodiments, thebasis weight of one or more layers (or the combination of two or morelayers) of a filter media is less than about 100 g/m², less than about90 g/m², less than about 80 g/m², less than about 70 g/m², less thanabout 60 g/m², less than about 50 g/m², less than about 40 g/m², lessthan about 30 g/m², less than about 20 g/m², or less than about 10 g/m².

In one particular set of embodiments, a filter media includes a firstlayer (e.g., a pre-filter layer) having a basis weight of between 5 g/m²and 70 g/m², e.g., between 40 g/m² and 60 g/m². The filter media mayinclude a second layer (e.g., a first main filter layer) adjacent (e.g.,directly adjacent) the first layer and have a basis weight between 5g/m² and 70 g/m², e.g., between 30 g/m² and 40 g/m². In some cases, thefilter media includes a third layer (e.g., a second main filter layer)adjacent (e.g., directly adjacent) the second layer, the third layerhaving a basis weight between 5 g/m² and 70 g/m², e.g., between 30 g/m²and 40 g/m². Additional layers are also possible.

Generally, the ratio of basis weights between two different layers of afilter media (e.g., between a first layer and a second layer, between asecond layer and a third layer, between a first layer and a third layer,etc.) can vary depending on the desired properties of the filter media.In some embodiments, an upstream layer of a filter media (e.g., apre-filter layer) has a larger basis weight than that of a downstreamlayer (e.g., a main filter layer). For example, the ratio of basisweights between an upstream layer and a downstream layer may be greaterthan 1:1, greater than 1.5:1, or greater than 2:1. In other embodiments,however, an upstream layer of a filter media has a smaller basis weightthan that of a downstream layer, e.g., the ratio of basis weightsbetween an upstream layer and a downstream layer may be less than 2:1,less than 1.5:1, or less than 1:1. In certain embodiments, the basisweight ratio of an upstream and a downstream layer is 1:1.

Thickness, as referred to herein, is determined according to TAPPI T411using an appropriate caliper gauge (e.g., a Model 200-A electronicmicrogauge manufactured by Emveco, tested at 1.5 psi). The overallthickness of a filter media may be between about 5 mils and 300 mils,e.g., between about 50 mils and 200 mils. The thickness of a layer ofthe filter media may be between about 3 mils and 100 mils, between about3 mils and 70 mils, between about 3 mils and 60 mils, between about 3mils and 50 mils, between about 3 mils and 40 mils, between about 3 milsand 30 mils, between about 3 mils and 20 mils, or between about 3 milsand 10 mils.

In one particular set of embodiments, a filter media includes a firstlayer (e.g., a pre-filter layer) having a thickness of between about 3mils and 70 mils, e.g., between about 15 mils and 20 mils. The filtermedia may include a second layer (e.g., a main filter layer) having athickness of between about 3 mils and 60 mils, e.g., between about 5mils and 10 mils. The filter media may optionally include a third layer(e.g., downstream of the second layer) having a thickness of betweenabout 3 mils and 60 mils, e.g., between about 5 mils and 10 mils.Additional layers are also possible.

The air permeability of filter media 10 can usually be selected asdesired. In some embodiments, the overall permeability of the filtermedia, may range from between about 2 cubic feet per minute per squarefoot (cfm/sf) and about 250 cfm/sf, between about 7 cfm/sf and about 200cfm/sf, between about 15 cfm/sf and about 135 cfm/sf, between about 15cfm/sf and about 50 cfm/sf, between about 2 cfm/sf and about 50 cfm/sf,or between about 10 cfm/sf and about 40 cfm/sf. As determined herein,the permeability of the filter media is measured according to TAPPIMethod T251. The permeability of a filter media is an inverse functionof flow resistance and can be measured with a Frazier PermeabilityTester. The Frazier Permeability Tester measures the volume of air perunit of time that passes through a unit area of sample at a fixeddifferential pressure across the sample. Permeability can be expressedin cubic feet per minute per square foot at a 0.5 inch waterdifferential.

The permeability of each layer of filter media 10 can also vary. In someembodiments, one or more layers of the filter media (e.g., an upstreamlayer, a downstream layer, a first layer, a second layer, a third layer,etc.) has a permeability of between about 3 cfm/sf and about 4000cfm/sf, between about 15 cfm/sf and about 700 cfm/sf, between about 4cfm/sf and about 400 cfm/sf, between about 5 cfm/sf and about 250cfm/sf, between about 7 cfm/sf and about 200 cfm/sf, between about 150cfm/sf and about 250 cfm/sf, between about 15 cfm/sf and about 150cfm/sf, between about 15 cfm/sf and about 50 cfm/sf, or between about 4cfm/sf and about 60 cfm/sf.

In one particular set of embodiments, a multi-layered filter mediaincludes an overall permeability of between about 2 cfm/sf and about 200cfm/sf, e.g., between about 3 cfm/sf and about 50 cfm/sf. The filtermedia may include a first layer (e.g., a pre-filter layer) having apermeability of between about 3 cfm/sf and about 4000 cfm/sf, e.g.,between about 15 cfm/sf and about 700 cfm/sf. The filter media mayinclude a second layer (e.g., adjacent a pre-filter layer, if present)having a permeability of between about 4 cfm/sf and about 800 cfm/sf,e.g., between about 7 cfm/sf and about 400 cfm/sf. If the filter mediaincludes a third layer, the permeability of that layer may be betweenabout 2 cfm/sf and about 300 cfm/sf, e.g., between about 4 cfm/sf andabout 60 cfm/sf.

In certain embodiments, one or more layers of a filter media has apermeability greater than or equal to about 20 cfm/sf, greater than orequal to about 50 cfm/sf, greater than or equal to about 80 cfm/sf,greater than or equal to about 100 cfm/sf, greater than or equal toabout 130 cfm/sf, greater than or equal to about 160 cfm/sf, greaterthan or equal to about 190 cfm/sf, greater than or equal to about 210cfm/sf, greater than or equal to about 230 cfm/sf, or greater than orequal to about 250 cfm/sf. In other embodiments, one or more layers of afilter media has a permeability less than or equal to about 250 cfm/sf,less than or equal to about 220 cfm/sf, less than or equal to about 190cfm/sf, less than or equal to about 160 cfm/sf, less than or equal toabout 140 cfm/sf, less than or equal to about 120 cfm/sf, less than orequal to about 100 cfm/sf, less than or equal to about 80 cfm/sf, lessthan or equal to about 50 cfm/sf, or less than or equal to about 30cfm/sf. Typically, an upstream layer has a larger permeability (lowerresistance) and/or a smaller pressure drop than that of a downstreamlayer, although other configurations are possible.

In certain embodiments, an upstream layer (e.g., a pre-filter layer or atop layer of a main filter layer) of a filter media has a permeabilityof greater than or equal to about 100 cfm/sf, greater than or equal toabout 150 cfm/sf, or greater than or equal to about 200 cfm/sf, and adownstream layer has a permeability of less than or equal to about 200cfm/sf, less than or equal to about 150 cfm/sf, less than or equal toabout 100 cfm/sf, or less than or equal to about 50 cfm/sf.

Certain filter media can have relatively low resistance ratios orcertain ranges of resistance ratios between two layers that providefavorable filtration properties. For instance, the resistance ratiobetween a second layer, which includes fibers having a small averagediameter, and a first layer, which includes fibers having a relativelylarger average diameter, may be relatively low. In some cases, thesecond layer is downstream of the first layer as shown in FIG. 1. Forexample, in one particular embodiment, the second layer is a main filterlayer and the first layer is a pre-filter layer. In another embodiment,the second layer is a downstream main filter layer and the first layeris an upstream filter layer. Other combinations are also possible. Theresistance ratio between two layers (e.g., between a second layer and afirst layer, between a downstream layer and an upstream layer, between amain layer and a pre-filter layer, or between two main layers, etc.),calculated as the resistance of the layer having a relatively smalleraverage fiber diameter to the resistance of the layer having arelatively larger average fiber diameter, may be, for example, between0.5:1 and 15:1, between 1:1 and 10:1, between 1:1 and 7:1, between 1:1and 5:1, or between 1:1 and 3.5:1. In some cases, the resistance ratiobetween the two layers is less than 15:1, less than 12:1, less than10:1, less than 8:1, less than 6:1, less than 5:1,less than 4:1, lessthan 3:1, or less than 2:1, e.g., while being above a certain value,such as greater than 0.01:1, greater than 0.1:1, or greater than 1:1.Advantageously, certain ranges of resistance ratios (including lowresistance ratios in some embodiments) can result in the filter mediahaving favorable properties such as high dirt holding capacity and/orhigh efficiency, while maintaining a relatively low overall basisweight. Such characteristics can allow the filter media to be used in avariety of applications.

In one particular set of embodiments, the resistance ratio between amain filter layer and a pre-filter layer adjacent (e.g., directlyadjacent) the main filter layer of a filter media is between 0.5:1 and7:1, between 1:1 and 5:1, or between 1:1 and 3.5:1. If the filter mediaincludes another main filter layer, the resistance ratio between thedownstream main filter layer to the upstream main filter layer may bebetween 1:1 and 12:1, between 1:1 and 8:1, between 1:1 and 6:1, orbetween 1:1 and 4:1. Additional layers are also possible.

The resistance of a layer may be normalized against the basis weight ofthe layer to produce a normalized resistance (e.g., resistance of alayer divided by the basis weight of the layer). In some cases, anormalized resistance ratio between two layers, e.g., a second layer,which includes fibers having a small average diameter, and a firstlayer, which includes fibers having a relatively larger averagediameter, is relatively low. For example, in one particular embodiment,the second layer is a main filter layer and the first layer is apre-filter layer. In another embodiment, the second layer is adownstream main filter layer and the first layer is an upstream filterlayer. Other combinations are also possible. The normalized resistanceratio between two layers (e.g., between a second layer and a firstlayer, between a downstream layer and an upstream layer, between a mainlayer and a pre-filter layer, or between two main layers, etc.),calculated as the normalized resistance of the layer having a relativelysmaller average fiber diameter to the normalized resistance of the layerhaving a relatively larger average fiber diameter, may be, for example,between 1:1 and 15:1, between 1:1 and 10:1, between 1:1 and 8:1, between1:1 and 5:1, or between 1:1 and 3:1. In some cases, the normalizedresistance ratio between the two layers is less than 15:1, less than12:1, less than 10:1, less than 8:1, less than 6:1, less than 5:1, lessthan 4:1, less than 3:1, or less than 2:1, e.g., while being above acertain value, such as greater than 0.01:1, greater than 0.1:1, orgreater than 1:1.

In one particular set of embodiments, the normalized resistance ratiobetween a main filter layer and a pre-filter layer adjacent (e.g.,directly adjacent) the main filter layer of a filter media is between1:1 and 8:1, between 1:1 and 5:1, or between 1:1 and 3:1. If the filtermedia includes another main filter layer, the resistance ratio betweenthe downstream main filter layer to the upstream main filter layer maybe between 1:1 and 10:1, between 1:1 and 8:1, between 1:1 and 6:1,between 1:1 and 4:1, or between 3:1 and 4:1. Additional layers are alsopossible.

Filter media 10 can also have good dirt holding properties. For example,filter media 10 can have an overall dirt holding capacity (DHC) of atleast about 100 g/m², at least about 120 g/m², at least about 140 g/m²,at least about 160 g/m², at least about 180 g/m², at least about 200g/m², at least about 220 g/m², at least about 240 g/m², at least about260 g/m², at least about 280 g/m², or at least about 300 g/m². The dirtholding capacity, as referred to herein, is tested based on a MultipassFilter Test following the ISO 16889 procedure (modified by testing aflat sheet sample) on a Multipass Filter Test Stand manufactured by FTI.The testing uses ISO A3 Medium test dust manufactured by PTI, Inc. at anupstream gravimetric dust level of 10 mg/liter. The test fluid isAviation Hydraulic Fluid AERO HFA MIL H-5606A manufactured by Mobil. Thetest was run at a face velocity of 0.14 meters/min until a terminalpressure of 172 kPa above the baseline filter pressure drop is obtained.

The dirt holding capacity of a filter media can be normalized againstthe basis weight of the media to produce a specific capacity (e.g., dirtholding capacity of the media divided by the basis weight of the media).The specific capacity of the filter media described herein may range,for example, between 1.5 and 3.0, between 1.7 and 2.7, or between 1.8and 2.5. In certain embodiments, the specific capacity of a filter mediais greater than or equal to 1.5, greater than or equal to 1.6, greaterthan or equal to 1.7, greater than or equal to 1.8, greater than orequal to 1.9, greater than or equal to 2.0, greater than or equal to2.1, greater than or equal to 2.2, greater than or equal to 2.3, greaterthan or equal to 2.4, greater than or equal to 2.5, greater than orequal to 2.6, greater than or equal to 2.7, greater than or equal to2.8, greater than or equal to 2.9, or greater than or equal to 3.0.

The dirt holding capacity of a filter media may also be normalizedagainst the overall basis weight of the media and the log of thefiltration ratio (Beta_((x))) for certain particle sizes “x” or greaterto produce a unitless value, “Absolute specific capacity at x microns”.For example, for a filter media that captures particle sizes of 10microns or greater and which has a certain Beta₍₁₀₎ value, the “Absolutespecific capacity at 10 microns” for that media would be calculated bymultiplying the dirt holding capacity of the media by the square root ofthe log of the Beta_((x)) value for 10 micron and larger particles, anddividing by the overall basis weight of the media.

In certain embodiments, a filter media having two (or more) layers hasan absolute specific capacity at 10 microns of greater than about 2.5,greater than about 2.65, greater than about 2.7, greater than about2.75, greater than about 3.0, greater than about 3.4, greater than about3.5, greater than about 3.6, greater than about 3.75, greater than about4.0, greater than about 4.25, greater than about 4.5, greater than about4.75, or greater than about 5.0. The filter media may additionally havea total basis weight of, for example, less than about 200 g/m², lessthan about 150 g/m², less than about 100 g/m², less than about 90 g/m²,less than about 80 g/m², less than about 75 g/m², less than about 70g/m², less than about 68 g/m², less than about 65 g/m²,less than about60 g/m², or less than about 50 g/m². Other values and ranges of absolutespecific capacity and basis weight are also possible.

In certain embodiments, a filter media having three (or more) layers hasan absolute specific capacity at 10 microns of greater than about 2.0,greater than about 2.25, greater than about 2.5, greater than about 2.6,greater than about 2.65, greater than about 2.75, greater than about3.0, greater than about 3.5, greater than about 3.75, greater than about4.0, greater than about 4.25, or greater than about 4.5. The filtermedia may additionally have a total basis weight of, for example, lessthan about 200 g/m², less than about 190 g², less than about 180 g/m²,less than about 170 g/m² , less than about 160 g/m², less than about 150g/m² , less than about 140 g/m², less than about 130 g/m², less thanabout 120 g/m², less than about 110 g/m², less than about 100 g/m², lessthan about 90 g/m², or less than about 80 g/m². Other values and rangesof absolute specific capacity and basis weight are also possible.

The filter media described herein may be used for the filtration ofvarious particle sizes, e.g., particles having a size of less than orequal to about 20 microns, less than or equal to about 15 microns, lessthan or equal to about 10 microns, less than or equal to about 5microns, less than or equal to about 3 microns, or less than or equal toabout 1 micron. The efficiency of filtering such particle sizes can bemeasured using a Multipass Filter Test. For instance, the efficiencyvalues were determined following the ISO 16889 procedure (modified bytesting a flat sheet sample) on a Multipass Filter Test Standmanufactured by FTI. The testing uses ISO A3 Medium test dustmanufactured by PTI, Inc. at an upstream gravimetric dust level of 10mg/liter. The test fluid is Aviation Hydraulic Fluid AERO HFA MILH-5606A manufactured by Mobil. The test was run at a face velocity of0.14 meters/min until a terminal pressure of 172 kPa above the baselinefilter pressure drop is obtained. Particle counts (particles permilliliter) at the particle sized selected (e.g., 1, 3, 4, 5, 7, 10, 15,20, 25, or 30 microns) upstream and downstream of the media can be takenat ten points equally divided over the time of the test. The average ofupstream and downstream particle counts can be taken at each selectedparticle size. From the average particle count upstream (injected −C₀)and the average particle count downstream (passed thru−C) the liquidfiltration efficiency test value for each particle size selected can bedetermined by the relationship [(100−[C/C₀])*100%].

Efficiency can also be expressed in terms of a Beta value (or Betaratio), where Beta_((x))=y is the ratio of upstream count (C₀) todownstream count (C), and where x is the minimum particle size that willachieve the actual ratio of C₀ to C that is equal to y. The penetrationfraction of the media is 1 divided by the Beta_((x)) value (y), and theefficiency fraction is 1−penetration fraction. Accordingly, theefficiency of the media is 100 times the efficiency fraction, and100*(1−1/Beta_((x)))=efficiency percentage. For example, a filter mediahaving a Beta_((x))=200 has an efficiency of [1−(1/200)]*100, or 99.5%for x micron or greater particles. The filter media described herein mayhave a wide range of Beta values, e.g., a Beta_((x))=y, where x can be,for example, 1, 3, 5, 7, 10, 12, 15, 20, 25, 30, 50, 70, or 100, andwhere y can be, for example, 2, 10, 75, 100, 200, or 1000. It should beunderstood that other values of x and y are also possible; for instance,in some cases, y may be greater than 1000. It should also be understoodthat for any value of x, y may be any number (e.g., 10.2, 12.4)representing the actual ratio of C₀ to C. Likewise, for any value of y,x may be any number representing the minimum particle size that willachieve the actual ratio of C₀ to C that is equal to y.

The filter media may be produced using processes based on knowntechniques. In some cases, the filter media is produced using a wet laidor a dry laid process. In general, a wet laid process involves mixingtogether the fibers; for example, glass fibers (e.g., chopped strandand/or microglass) may be mixed together, optionally with any syntheticfibers, to provide a glass fiber slurry. In some cases, the slurry is anaqueous-based slurry. In certain embodiments, the microglass fibers, andoptionally any chopped strand and/or synthetic fibers, are storedseparately in various holding tanks prior to being mixed together. Thesefibers may be processed through a pulper before being mixed together. Insome embodiments, combinations of chopped strand glass fibers,microglass fibers, and/or synthetic fibers are processed through apulper and/or a holding tank prior to being mixed together. As discussedabove, microglass fibers may include fine microglass fibers and coarsemicroglass fibers.

It should be appreciated that any suitable method for creating a glassfiber slurry may be used. In some cases, additional additives are addedto the slurry to facilitate processing. The temperature may also beadjusted to a suitable range, for example, between 33° F. and 100° F.(e.g., between 50° F. and 85° F.). In some embodiments, the temperatureof the slurry is maintained. In some cases, the temperature is notactively adjusted.

In some embodiments, the wet laid process uses similar equipment as aconventional papermaking process, which includes a hydropulper, a formeror a headbox, a dryer, and an optional converter. For example, theslurry may be prepared in one or more pulpers. After appropriatelymixing the slurry in a pulper, the slurry may be pumped into a headbox,where the slurry may or may not be combined with other slurries oradditives may or may not be added. The slurry may also be diluted withadditional water such that the final concentration of fiber is in asuitable range, such as for example, between about 0.1% to 0.5% byweight.

In some cases, the pH of the glass fiber slurry may be adjusted asdesired. For instance, the pH of the glass fiber slurry may rangebetween about 1.5 and about 4.5, or between about 2.6 and about 3.2.

Before the slurry is sent to a headbox, the slurry may be passed throughcentrifugal cleaners for removing unfiberized glass or shot. The slurrymay or may not be passed through additional equipment such as refinersor deflakers to further enhance the dispersion of the fibers. Fibers maythen be collected on a screen or wire at an appropriate rate using anysuitable machine, e.g., a fourdrinier, a rotoformer, a cylinder, or aninclined wire fourdrinier.

In some embodiments, the process involves introducing binder (and/orother components) into a pre-formed glass fiber layer. In someembodiments, as the glass fiber layer is passed along an appropriatescreen or wire, different components included in the binder, which maybe in the form of separate emulsions, are added to the glass fiber layerusing a suitable technique. In some cases, each component of the binderresin is mixed as an emulsion prior to being combined with the othercomponents and/or glass fiber layer. In some embodiments, the componentsincluded in the binder may be pulled through the glass fiber layerusing, for example, gravity and/or vacuum. In some embodiments, one ormore of the components included in the binder resin may be diluted withsoftened water and pumped into the glass fiber layer.

As noted above, different layers of glass fibers may be combined toproduce filter media based on desired properties. For example, in someembodiments, a relatively coarser pre-filter layer may be combined witha relatively finer fiber layer (i.e., a main filter layer) to form amulti-layered filter media. Optionally, the filter media can include oneor more additional finer fiber layers as described above.

Multi-phase filter media may be formed in an appropriate manner. As anexample, a filter media or a portion thereof may be prepared by a wetlaid process where a first glass fiber slurry (e.g., glass fibers in anaqueous solvent such as water) is applied onto a wire conveyor to form afirst layer. A second glass fiber slurry (e.g., glass fibers in anaqueous solvent such as water) is then applied onto the first layer.Vacuum may be continuously applied to the first and second slurriesduring the above process to remove solvent from the fibers, resulting inthe simultaneous formation of the first and second layers into acomposite article. The composite article is then dried. Due to thisfabrication process, at least a portion of the fibers in the first layercan be intertwined with at least a portion of the fibers from the secondlayer (e.g., at the interface between the two layers). Additional layerscan also be formed and added using a similar process or a differentprocess such as lamination, co-pleating, or collation (i.e., placeddirectly adjacent one another and kept together by pressure). Forexample, in some cases, two layers (e.g., two fine fiber layers) areformed into a composite article by a wet laid process in which separatefiber slurries are laid one on top of the other as water is drawn out ofthe slurry, and the composite article is then combined with a thirdlayer (e.g., a pre-filter layer) by any suitable process (e.g.,lamination, co-pleating, or collation). It can be appreciated thatfilter media or composite article formed by a wet laid process may besuitably tailored not only based on the components of each fiber layer,but also according to the effect of using multiple fiber layers ofvarying properties in appropriate combination to form filter mediahaving the characteristics described herein.

In one set of embodiments, at least two layers of a filter media (e.g.,a layer and a composite article comprising more than one layer, or twocomposite articles comprising more than one layer) are laminatedtogether. For instance, a first layer (e.g., a prefilter layer includingrelatively coarse fibers) may be laminated with a second layer (e.g., amain filter layer including relatively fine fibers), where the first andsecond layers face each other to form a single, multilayer article(e.g., a composite article) that is integrally joined in a singleprocess line assembly operation to form the filter media. If desired,the first and second layers can be combined with another main filterlayer (e.g., a third layer) using any suitable process before or afterthe lamination step. In other embodiments, two or more layers (e.g.,main filter layers) are laminated together to form a multilayer article.After lamination of two or more layers into a composite article, thecomposite article may be combined with additional layers via anysuitable process.

In other embodiments, a dry laid process is used. In a dry laid process,glass fibers are chopped and dispersed in air that is blown onto aconveyor, and a binder is then applied. Dry laid processing is typicallymore suitable for the production of highly porous media includingbundles of glass fibers.

During or after formation of a layer, a composite article including twoor more combined layers, or a final filter media, the layer, compositearticle or final filter media may be further processed according to avariety of known techniques. For example, the filter media or portionsthereof may be pleated and used in a pleated filter element. Forinstance, two layers may be joined by a co-pleating process. In someembodiments, filter media, or various layers thereof, may be suitablypleated by forming score lines at appropriately spaced distances apartfrom one another, allowing the filter media to be folded. It should beappreciated that any suitable pleating technique may be used. Thephysical and mechanical qualities of the filter media can be tailored toprovide, in some embodiments, an increased number of pleats, which maybe directly proportional to increased surface area of the filter media.The increased surface area may allow the filter media to have anincreased filtration efficiency of particles from fluids. For example,in some cases, the filter media described herein includes 2-12 pleatsper inch, 3-8 pleats per inch, or 2-5 pleats per inch. Other values arealso possible.

It should be appreciated that the filter media may include other partsin addition to the two or more layers described herein. In someembodiments, further processing includes incorporation of one or morestructural features and/or stiffening elements. For instance, the mediamay be combined with additional structural features such as polymericand/or metallic meshes. In one embodiment, a screen backing may bedisposed on the filter media, providing for further stiffness. In somecases, a screen backing may aid in retaining the pleated configuration.For example, a screen backing may be an expanded metal wire or anextruded plastic mesh.

As previously indicated, the filter media disclosed herein can beincorporated into a variety of filter elements for use in variousapplications including hydraulic and non-hydraulic filtrationapplications. Exemplary uses of hydraulic filters (e.g., high-, medium-,and low-pressure filters) include mobile and industrial filters.Exemplary uses of non-hydraulic filters include fuel filters (e.g.,automotive fuel filters), oil filters (e.g., lube oil filters or heavyduty lube oil filters), chemical processing filters, industrialprocessing filters, medical filters (e.g., filters for blood), airfilters, and water filters. In some cases, filter media described hereincan be used as coalescer filter media.

In some cases, the filter element includes a housing that may bedisposed around the filter media. The housing can have variousconfigurations, with the configurations varying based on the intendedapplication. In some embodiments, the housing may be formed of a framethat is disposed around the perimeter of the filter media. For example,the frame may be thermally sealed around the perimeter. In some cases,the frame has a generally rectangular configuration surrounding all foursides of a generally rectangular filter media. The frame may be formedfrom various materials, including for example, cardboard, metal,polymers, or any combination of suitable materials. The filter elementsmay also include a variety of other features known in the art, such asstabilizing features for stabilizing the filter media relative to theframe, spacers, or any other appropriate feature.

In one set of embodiments, the filter media described herein isincorporated into a filter element having a cylindrical configuration,which may be suitable for hydraulic and other applications. Thecylindrical filter element may include a steel support mesh that canprovide pleat support and spacing, and which protects against mediadamage during handling and/or installation. The steel support mesh maybe positioned as an upstream and/or downstream layer. The filter elementcan also include upstream and/or downstream support layers that canprotect the filter media during pressure surges. These layers can becombined with filter media 10, which may include two or more layers asnoted above. The filter element may also have any suitable dimensions.For example, the filter element may have a length of at least 15 inches,at least 20 inches, at least 25 inches, at least 30 inches, at least 40inches, or at least 45 inches. The surface area of the filter media maybe, for example, at least 220 square inches, at least 230 square inches,at least 250 square inches, at least 270 square inches, at least 290square inches, at least 310 square inches, at least 330 square inches,at least 350 square inches, or at least 370 square inches.

The filter elements may have the same property values as those notedabove in connection with the filter media. For example, the above-notedresistance ratios, basis weight ratios, dirt holding capacities,efficiencies, specific capacities, and fiber diameter ratios betweenvarious layers of the filter media may also be found in filter elements.

During use, the filter media mechanically trap particles on or in thelayers as fluid flows through the filter media. The filter media neednot be electrically charged to enhance trapping of contamination. Thus,in some embodiments, the filter media are not electrically charged.However, in some embodiments, the filter media may be electricallycharged.

The following examples are intended to illustrate certain embodiments ofthe present invention, but are not to be construed as limiting and donot exemplify the full scope of the invention.

EXAMPLE 1

This example describes the formation of several multi-layered filtermedia and their characterization according to various embodiments of theinvention.

Two- and three-layered filter media were prepared according to thespecifications listed in Table 1. The two-layered filter media (Samples2A, 2B, and 3) included a first main filter layer (denoted topphase-main filter layer in Table 1) and a second main filter layer(bottom phase-main filter layer) adjacent the first layer.

The two-layered media was formed by a wet laid papermaking process.Briefly, for one layer, 250 gallons of water was added to a hydropulper,then sulfuric acid was added to bring the pH to approximately 3.0.Fibers were added to the mixture, and the fiber and water slurry wasmixed for 4 minutes. The slurry was then pumped to a first holding chestwith 900 gallons of additional water. For the second layer, this processwas repeated with the fibers needed for the second layer, and the slurrywas pumped to a different holding chest.

Slurry from the first holding chest was pumped to the main headbox of afourdrinier papermachine, along with additional water and additionalsulfuric acid to reduce the pH to about 2.6. The slurry was allowed toflow onto the forming wire of the papermachine and water was drained bygravity, as well as by a series of vacuum slots eventually forming awet, loosely bound web of fibers which was carried away by the movingforming wire. To make the second layer, fiber from the second holdingchest was pumped, along with dilution water, to a secondary headbox alsolocated on the fourdrinier papermaking machine. The secondary headboxwas positioned so that the forming wire carrying the drained fibers fromthe main headbox passed underneath the secondary headbox. The secondslurry laid on top of, and then drained through, the already formed webfrom the primary headbox. The water was then removed by another seriesof vacuum slots resulting in a combined single web including fibers fromthe main headbox as a bottom layer and fibers from the secondary headboxas a top layer. This combined single web was then sprayed with a latexsolution to add organic binder. The web was then dried by passing over aseries of steam filled dryer cans. The now dry web is wound into rollsat a reel.

The three-layered filter media (Samples 1, 4A, 4B, 5A and 5B) included apre-filter layer as a first layer (pre-filter-single phase), a mainfilter layer as the second layer (top phase-main filter layer) adjacentthe first layer, and another main filter layer (bottom phase-main filterlayer) adjacent the second layer. Prior to assembly with the firstlayer, the second and third layers were formed simultaneously into acomposite article using the same wet laid process as for the two-layeredmedia. The first layer was then assembled with the composite article bycollation.

TABLE 1 Comparison of various two- and three-layered filter media SampleSample Sample Sample Sample Sample Sample 1 (three 2A 2B Sample 3 4A(three 4B (three 5A (three 5B (three layer (two layer (two layer (twolayer layer layer layer layer Characteristics and Parameters media)media) media) media) media) media) media) media) Physical OverallCaliper (inches) 0.035 N.A. N.A. N.A. N.A. N.A. N.A. N.A. AttributesTotal BW (lbs/3000 ft²) 70 40 40 40 70 70 70 70 Total BW (g/m²) 114 6565 65 114 114 114 114 Total Permeability (ft²/min/ft²) 21 −26 −27 −15−20 −20 −20 −20 Pre-Filter (Single Phase) BW (lb/3000 ft²) 30 NA NA NA30 30 30 30 Grammage (g/m²) 49 49 49 49 49 Permeability 232 152 304 76608 Top Phase - Main Filter Layer BW (lb/3000 ft²) 20 20 20 20 20 20 2020 Grammage (g/m²) 33 33 33 33 33 33 33 33 Permeability 118 114 153 59114 114 114 114 Bottom Phase - Main Filter Layer BW (lb/3000 ft²) 20 2020 20 20 20 20 20 Grammage (g/m²) 33 33 33 33 33 33 33 33 Permeability38 38 38 37 36 36 36 36 Furnish Overall Glass 93% glass 93% glass 93%glass 93% glass 93% glass 93% glass 93% glass 93% glass Organic 7% 7% 7%7% 7% 7% 7% 7% organic organic organic organic organic organic organicorganic Pre-Filter (Single Phase) Composition Total Glass Content(diameter) 92% NA 92% 92% 92% 92% JM Code 108A (1.0 microns) EFC Code309 (1.9 microns) EFC Code 310 (3.0 microns) 92% EFC Code 312 (3.9microns) 92% EFC Code 316 (5.2 microns) 92% EFC Code 717 (6.1 microns)92% EFC Code 718 (5.8 microns) EFC Code 719 (8.5 microns) 92% TotalOrganic Content  8%  8%  8%  8%  8% Polyester Fiber Liquid Binder  5% 5%  5%  5%  5% Kuralon Fiber  3%  3%  3%  3%  3% Top Phase - MainFilter Layer Total Glass Content (diameter) 92% 92% 92% 92% 92% 92% 92%92% JM Code 108A (1.0 microns) EFC Code 309 (1.9 microns) 92% EFC Code310 (3.0 microns) 92% 92% 46% 92% 92% EFC Code 312 (3.9 microns) 46% EFCCode 316 or 716 (5.2 microns) EFC Code 717 (6.1 microns) 92% 92% EFCCode 718 (5.8 microns) EFC Code 719 (8.5 microns) Total Organic Content 8%  8%  8%  8%  8%  8%  8%  8% Polyester Fiber (0.6 Denier) LiquidBinder  5%  5%  5%  5%  5%  5%  5%  5% Kuralon Fiber  3%  3%  3%  3%  3% 3%  3%  3% Bottom Phase - Main Filter Layer Total Glass Content(diameter) 94% 94% 94% 94% 94% 94% 94% 94% JM Code 108A (1.0 microns)46% 42% 42% 42% 46% 46% 46% 46% EFC Code 309 (1.9 microns) 16% 17% 17%17% 16% 16% 16% 16% EFC Code 310 (3.0 microns) EFC Code 312 (3.9microns) 16% 17% 17% 17% 16% 16% 16% 16% EFC Code 316 or 716 (5.2microns) EFC Code 717 (6.1 microns) EFC Code 718 (5.8 microns) 16% 17%17% 17% 16% 16% 16% 16% EFC Code 719 (8.5 microns) Total Organic Content 6%  6%  6%  6%  6%  6%  6%  6% Polyester Fiber (0.5 Denier) LiquidBinder  4%  4%  4%  4%  4%  4%  4%  4% Kuralon Fiber  2%  2%  2%  2%  2% 2%  2%  2% Performance Overall Dirt Holding Capacity (g/m²) 225.0 177.0169.0 117.0 221.0 203.0 103.0 170.0 Attributes Overall Beta_((x)) = 200(μm_(c)) 8.6 10.1 10.0 8.1 8.8 8.3 7.1 7.8 Absolute Specific Capacity @10 μm_((c)) 3.3 2.6 2.5 2.0 3.2 3.1 1.7 2.7 Actual Resistance Ratio: TopPhase 2.0 N.A. N.A. N.A. 1.3 2.7 0.7 5.3 Main Filter/Pre-Filter ActualResistance Ratio: Bottom 3.3 3.0 4.1 1.6 N.A. N.A. N.A. N.A. Phase/TopPhase - Main Filter Additional Overall Dirt Holding Capacity (g/m²)225.0 177.0 169.0 117.0 221.0 203.0 103.0 170.0 Performance SpecificCapacity (g dust/g media) 1.97 2.72 2.60 1.80 1.94 1.78 0.90 1.49Attributes Overall Beta_((x)) = 200 (μm_(c)) 8.6 10.1 10.0 8.1 8.8 8.37.1 7.8 Normalized Resistance Ratio: Top 2.9 N.A. N.A. N.A. 2.0 4.0 1.08.0 Phase Main Filter/Pre-Filter Normalized Resistance Ratio: Bottom 3.33.0 4.1 1.6 N.A. N.A. N.A. N.A. Phase/Top Phase - Main Filter

EXAMPLE 2

This example describes the formation of several single- andmulti-layered filter media and their characterization.

Table 2 includes various comparative samples having Beta_((x))=1000,where x is about 4 to 4.5 microns. Comparative Sample 1A had a first(upstream) layer and a second (downstream) layer, the second layerhaving finer fibers than the first layer. The particular compositions ofthe first and second layers of Comparative Sample 1A are included inTable 4. The first and second layers were formed using the handsheetprotocol described below. Comparative Samples 2-10 are commercial gradesfrom Hollingsworth and Vose Company. As shown in Table 2, all of thecomparative samples had absolute specific capacity at 10 μm values ofless than 2.7.

TABLE 2 Characteristics for various single- and multi-layered filtermedia Absolute Resistance Resistance Specific BW BW Ratio Ratio Beta =Capacity @ Sample (lbs/r) (g/m²) CFM (as is) (normalized) Capacity 100010 μm_((c)) Comparative Sample 1A (2 layers, handsheet) 50.3 81.8 6.80.02 0.01 88.09 4.1 1.97 Comparative Sample 2 (HC4683, Single Layer)47.7 77.6 7.5 87.35 4.3 2.17 Comparative Sample 3 (HC4683, Single Layer)47.8 77.7 7.4 84.03 4.4 2.08 Comparative Sample 4 (HC4683, Single Layer)47.9 77.9 7.6 90.64 4.4 2.24 Comparative Sample 5 (HB7633, Single Layer)49.2 80.0 6.8 82.73 4.4 1.94 Comparative Sample 6 (DC4271, 2 layers)53.8 87.5 7.38 114.24 4.5 2.60 Comparative Sample 7 (DC4271, 2 layers)53.8 87.5 7.18 115.25 4.5 2.68 Comparative Sample 8 (DC4271, 2 layers)54.1 88.0 7.21 121.67 4.5 2.58 Comparative Sample 9 (DC4271, 2 layers)53.6 87.2 7.72 119.31 4.6 2.68 Comparative Sample 10 (DC4271, 2 layers)54.7 88.9 7.56 116.96 4.6 2.66

Table 3 includes various comparative samples having Beta_((x))=200,where x is about 6 to 7 microns. Comparative Sample 1B had the samecomposition as that of Comparative Sample 1A, except the first andsecond layers were reversed. That is, Comparative Sample 1B had a first(upstream) layer and a second (downstream) layer, the first layer havingfiner fibers than the second layer. The first and second layers wereformed using the handsheet protocol described below.

Comparative Samples 11-18 are commercial grades from Hollingsworth andVose Company.

Samples 6-9 are two-layered filter media having various physicalcharacteristics and performance characteristics according certainembodiments of the invention.

As shown in Table 2, all of the comparative samples had absolutespecific capacity at 10 μm values of less than 3.4, while Samples 6-9had values of greater than 3.4.

TABLE 3 Characteristics for various single- and multi-layered filtermedia Absolute Resistance Resistance Specific BW BW Ratio (as Ratio Beta= Capacity @ Sample (lb/r) (g/m²) CFM is) (normalized) Capacity 200 10μm_((c)) Comparative Sample 1B (2 layers, handsheet) 48.2 78.4 0.2 0.020.01 77.45 6.2 1.56 Comparative Sample 11 (KE1071, Single Layer) 38.162.0 15.4 105.88 6.3 3.29 Comparative Sample 12 (KE1071, Single Layer)38.6 62.8 16 104.01 6.3 3.18 Comparative Sample 13 (KE1071, SingleLayer) 38.2 62.1 15.7 100.95 6.4 3.01 Comparative Sample 14 (KE1071,Single Layer) 38.3 62.3 23.4 97.39 6.4 2.96 Comparative Sample 15(KE1071, Single Layer) 38.5 62.6 15.5 105.09 6.4 3.32 Comparative Sample16 (KE1071, Single Layer) 38.3 62.3 21.2 99.95 6.4 3.16 ComparativeSample 17 (KE1071, Single Layer) 38.1 62.0 21.3 99.27 6.5 3.13Comparative Sample 18 (KE1071, Single Layer) 38.4 62.4 15.6 100.44 6.53.07 Sample 6 (2 layers, Pilot Trial) 39.7 64.6 22.5 148.47 7.8 4.14Sample 7 (2 layers, Pilot Trial) 40.9 66.5 21 140.39 7.7 3.84 Sample 8(2 layers, Paper Machine) 41.4 67.3 17.7 125.29 7.1 3.53 Sample 9 (2layers, Paper Machine) 41.5 67.5 17.8 125.28 7.2 3.49

The samples labeled “handsheet” in Tables 2 and 3 were formed by awet-laid handsheet making process. The handsheet mold was prepared usingstandard procedures. To form a first layer, 5 mL of 25% sulfuric acidwas used to acidify the entire volume of the handsheet mold to a pH of3.0. From this prepared handsheet mold, 750 mL of acidified water wasobtained and placed in a Waring 1-speed glass blender. A Variac settingof 60 was used for the pulping level. 4.53 grams of Code 112 fibers and0.5 grams chopped strand fibers were added to the blender and pulpeduntil well dispersed (˜60 seconds). The fiber and water slurry are thenadded to the top of the handsheet mold, the slurry agitated and thendrained through the forming wire. The wet sheet is then vacuumed anddried on a photodryer.

The second layer required a modification to the handsheet methoddescribed above in that the previously formed first layer was used as abottom layer sheet, and was placed on the handsheet mold and supportedon the edges with blotter paper. The handsheet mold was clamped down andwater was carefully added on the side of the mold so as not to disturbthe now wet sheet. The water was again acidified with 5 mL of 25%sulfuric acid and 750 mL withdrawn for the secondary layer mixture. Thepreviously weighed 2.42 grams of Code 104 fiber was blended in a Waring1-speed glass blender for ˜60 seconds and then added to the top of thehandsheet mold. The slurry was then carefully agitated so as not todisturb the wet bottom layer and the slurry then drained through theprimary layer and the forming wire. The two layer handsheet was thenvacuumed and dried on a photodryer.

Samples 6 and 7 were formed using the method described in Example 1.

The commercial grade comparative samples shown in Tables 2 and 3, aswell as Samples 8 and 9, were formed using a paper machine process.Briefly, for one layer, about 1000 gallons of water was added to ahydropulper, then 2 quarts of sulfuric acid was added to bring the pH toapproximately 3.0. Fibers were added to the mixture, along with 1000gallons of water, and the fiber and water slurry was mixed for 5minutes. The slurry was then pumped to a first holding chest with 4700gallons of additional water.

For two-layer media, this process was repeated with the fibers neededfor the second layer, except 5000 gallons of water was added instead of4700 gallons before being pumped to a different holding chest.

Slurry from the first holding chest was pumped to the main headbox of afourdrinier papermachine, along with additional water and additionalsulfuric acid to reduce the pH to about 2.6. The slurry was allowed toflow onto the forming wire of the papermachine and water was drained bygravity, as well as by a series of vacuum slots eventually forming awet, loosely bound web of fibers which was carried away by the movingforming wire. To make the second layer, fiber from the second holdingchest was pumped, along with dilution water, to a secondary headbox alsolocated on the fourdrinier papermaking machine. The secondary headboxwas positioned so that the forming wire carrying the drained fibers fromthe main headbox passed underneath the secondary headbox. The secondslurry laid on top of, and then drained through, the already formed webfrom the primary headbox. The water was then removed by another seriesof vacuum slots resulting in a combined single web including fibers fromthe main headbox as a bottom layer and fibers from the secondary headboxas a top layer. The combined web was then dried by passing over a seriesof steam filled dryer cans. The now dry web is wound into rolls at areel.

TABLE 4 Composition of Comparative Samples 1A and 1B Top Bottom Layer BWBW Layer BW BW Sample Furnish Grams (lbs/r) (g/m²) Furnish Grams (lbs/r)(g/m²) Comparative Samples 1A JM Code 112 4.53 33.2 54.0 JM Code 2.4216.0 26.0 and 1B (90%) 0.50 104 JM Chop Pak A20 ½″ (10%)

EXAMPLE 3

This example describes the characterization of several single- andmulti-layered filter media.

FIG. 2 shows the absolute specific capacity at 10 μm for various filtermedia plotted against the overall basis weight of the media. The basisweights were plotted on a log scale.

Comparative Sample Sets 19 and 20 are two- and three-layered media,respectively.

Sample Set 10 are two-layered media formed by the wet laid processdescribed in Example 1. Sample Set 11 are three-layered media includinga pre-filter layer, a first main filter layer, and a second main filterlayer. The first and second main filter layers were fabricated using thewet laid process described in Example 1 to form a composite article,which was then collated to a pre-filter layer.

As shown in FIG. 2, Sample Set 10 (two-layered media) had higherabsolute specific capacity at 10 μm values and lower basis weights thanthose of Comparative Sample Set 19 (two-layered media). For instance,the filter media of Sample Set 10 had absolute specific capacity at 10μm values of greater than 3.4 while having a basis weight of less than75 g/m². By contrast, the filter media of Comparative Sample Set 19 hadabsolute specific capacity at 10 μm values of less than 3.4 while havinga basis weight of greater than 75 g/m².

Additionally, Sample Set 11 (three-layered media) had higher absolutespecific capacity at 10 μm values and lower basis weights than thefilter media of Comparative Sample Set 20 (three-layered media). Forinstance, the filter media of Sample Set 11 had absolute specificcapacity at 10 μm values of greater than 2.65. By contrast, the filtermedia of Comparative Sample Set 20 had absolute specific capacity at 10μm values of less than 2.65. The basis weights of the Sample Set 11media was lower than those of the media of Comparative Sample Set 20.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1. A filter media comprising: a first layer comprising glass fibers, thefibers in the first layer having a first average diameter; a secondlayer comprising glass fibers, the fibers in the second layer having asecond average diameter, wherein the second average diameter is smallerthan the first average diameter, a third layer comprising glass fibers,the fibers in the third layer having a third average diameter, whereinthe third average diameter is smaller than the second average diameter,wherein the second layer is directly adjacent the first and third filterlayers, and wherein a normalized resistance ratio of the second layer tothe first layer is between 1:1 and 15:1.
 2. A filter media as in claim1, wherein the normalized resistance ratio of the second layer to thefirst layer is between 1:1 and 10:1.
 3. A filter media as in claim 1,wherein the normalized resistance ratio of the second layer to the firstlayer is between 1:1 and 5:1.
 4. A filter media as in claim 1, whereinthe first layer includes less than 5 wt % synthetic fibers.
 5. A filtermedia as in claim 1, wherein the first layer is a pre-filter layer andhas a basis weight greater than the basis weight of the second layer. 6.A filter media as in claim 1, wherein at least one of the first, secondand third layers comprises at least 90 wt % glass fibers.
 7. A filtermedia as in claim 1, wherein at least one of the first, second and thirdlayers comprises at least 90 wt % microglass fibers.
 8. A filter mediaas in claim 7, wherein the microglass fibers have an average diameter ofbetween 1 μm and 6 μm.
 9. A filter media as in claim 1, wherein theratio of first and second average diameters and/or the ratio of thirdand second average diameters is less than 2:1.
 10. A filter media as inclaim 1, wherein at least one of the first, second and third layers hasa basis weight of less than 40 g/m².
 11. A hydraulic filter elementcomprising the filter media of claim
 1. 12. A filter media comprising: afirst layer comprising at least 80 wt % glass fibers, wherein the fibersin the first layer have a first average diameter; and a second layerdirectly adjacent the first layer, the second layer comprising glassfibers, wherein the fibers in the second layer have a second averagediameter, wherein the second average diameter is smaller than the firstaverage diameter, and wherein a normalized resistance ratio of thesecond layer to the first layer is between 1:1 and 5:1.
 13. A filtermedia as in claim 12, wherein the first layer includes less than 5 wt %synthetic fibers.
 14. A filter media as in claim 12, wherein the firstlayer comprises at least 90 wt % glass fibers.
 15. A filter media as inclaim 12, wherein the second layer comprises at least 90 wt % glassfibers.
 16. A filter media as in claim 12, wherein the first and/orsecond layers comprises at least 90 wt % microglass fibers.
 17. A filtermedia as in claim 12, wherein the first layer is a pre-filter layer andhas a basis weight greater than the basis weight of the second layer.18. A filter media as in claim 12, further comprising a third layeradjacent the second layer.
 19. A filter media as in claim 12, whereinthe first layer is a pre-filter layer having coarser fibers than thesecond layer.
 20. A filter media as in claim 12, wherein each of thefirst and second average diameters are less than 10 μm.
 21. A filtermedia as in claim 12, wherein each of the first and second layersincludes microglass fibers having an average diameter of between 1 μmand 6 μm.
 22. A filter media as in claim 12, wherein the ratio of firstand second average diameters is less than 2:1.
 23. A filter media as inclaim 12, wherein the first and/or second layer has a basis weight ofless than 40 g/m².
 24. A filter media comprising: a first layercomprising glass fibers, the fibers in the first layer having a firstaverage diameter; a second layer adjacent the first layer comprisingglass fibers, the fibers in the second layer having a second averagediameter; and a third layer adjacent the second layer comprising glassfibers, the fibers in the third layer having a third average diameter,wherein the filter media has an absolute specific capacity at 10 micronsof greater than about 2.65.
 25. A filter media as in claim 24, whereinthe filter media has an absolute specific capacity at 10 microns ofgreater than about 2.75.
 26. A filter media as in claim 24, wherein thefilter media has an absolute specific capacity at 10 microns of greaterthan about 3.0.
 27. A filter media as in claim 24, wherein the filtermedia has an overall basis weight of about 150 g/m² or less.
 28. Afilter media as in claim 24, wherein the filter media has an overalldirt holding capacity of at least about 185 g/m².
 29. A filter media asin claim 24, wherein at least two layers are formed simultaneously toform a composite.
 30. A filter media comprising: a first layercomprising glass fibers, the fibers in the first layer having a firstaverage diameter; and a second layer adjacent the first layer comprisingglass fibers, the fibers in the second layer having a second averagediameter, wherein the first and second layers have a combined basisweight of less than 75 g/m² and an absolute specific capacity at 10microns of greater than about 3.4.
 31. A filter media as in claim 30,wherein the filter media has an absolute specific capacity at 10 micronsof greater than about 4.0.
 32. A filter media as in claim 30, whereinthe first and second layers have a combined basis weight of less than 70g/m² and an absolute specific capacity at 10 microns of greater thanabout 3.5.
 33. A filter media as in claim 30, wherein the first and/orsecond layer has a basis weight of less than 40 g/m².
 34. A filter mediaas in claim 30, wherein the ratio of first and second average diametersis less than 2:1.
 35. A filter media as in claim 30, further comprisinga third layer adjacent the second layer.
 36. A filter media comprising:a first layer comprising at least 90 wt % glass fibers, the first layerhaving a basis weight of greater than about 40 g/m²; a second layeradjacent the first layer comprising at least 90 wt % glass fibers, thesecond layer having a basis weight of less than about 40 g/m²; and athird layer adjacent the second layer comprising at least 90 wt % glassfibers.
 37. A filter media as in claim 36, wherein the first and/orsecond layers comprises at least 90 wt % microglass fibers.
 38. A filtermedia as in claim 36, wherein the second layer is immediately adjacentthe first and third layers.
 39. A filter media as in claim 36, whereinthe first, second and/or third layers comprises at least 93 wt % glassfibers.
 40. A method of filtering a liquid comprising: passing a liquidincluding particulates through a filter media comprising: a first layercomprising glass fibers, the fibers in the first layer having a firstaverage diameter; a second layer comprising glass fibers, the fibers inthe second layer having a second average diameter, wherein the secondaverage diameter is smaller than the first average diameter, a thirdlayer comprising glass fibers, the fibers in the third layer having athird average diameter, wherein the third average diameter is smallerthan the second average diameter, wherein the second layer is directlyadjacent the first and third filter layers, and wherein a normalizedresistance ratio of the second layer to the first layer is between 1:1and 15:1.